This brief report is a part of a USC Sedimentology and stratigraphybasins class assignment (GEOL325). The class members visited the preserve last week. Students are required to describe the outcrops and come up with a hypothesis regarding the depositional environment of the preserve based on exposed facies. Two plausible theories were proposed during the field trip. The first was that these outcrops represented a beach environment. The other hypothesis suggested that this was a flood tidal delta environment.

I personally think that the second hypothesis that this was floor tidal delta and was part of a transgressive barrier island depositional system is more plausible.

Background

Peach Tree Rock (photo 1) is a small nature preserve located just outside Lexington county, and a few minutes from Columbia Metropolitan Airport, South Carolina. (Check on Google Maps).

Photo 1: Peach Tree Rock

Most geologists agree that these outcrops are of top of middle Eocene (45 Million Years Ago) (Lucille, 1985) and were deposited when the sea level was about 125 meter higher than the present level. The outcrops at the Peach Tree Rock preserve are about 500' above sea level and are about 3-10 meters high.

Interpretations

The cross-bedding of sand of sand (fine to coarse) and burrowing indicated clearly that these rocks are of marine or near-shore environment (photo 2 & 3).

Most of the beds are dipping on both directions and some cut and fill structures are also visible. Thin laminations of containing clay and clay flake deposits are also scattered within the sand beds (photo 4).

Barrier-island complexes are typically the result of transgression (Boggs, 2001), which can be produced by landward advance of the shoreline owing to shoreface erosion (during slow rise of sea level). Flood-tidal delta occurs on the lagoonal side of the barrier island (see figure 1). Sandy deposits characterized by highly varied succession of planar and trough cross-beds sets that may dip in either a landward or a seaward direction (Boggs, 2001). The flood-tidal delta is only slightly influenced by wave and wind-generated processes (trace fossils and vertical burrows are also common in this environment.

Figure 1: A schematic of a barrier island system

and finally, a visit to Peach Tree preserve is not complete if the waterfall is not mentioned (photo 5).